Cyclone Hergen was an intense

European windstorm European windstorms are powerful extratropical cyclones which form as cyclonic windstorms associated with areas of low atmospheric pressure. They can occur throughout the year, but are most frequent between October and March, with peak inten ...

that moved across Northern Europe during mid December 2011. It was first noted over the central North Atlantic Ocean by the

Met Office The Meteorological Office, abbreviated as the Met Office, is the United Kingdom's national weather service. It is an executive agency and trading fund of the Department for Business, Energy and Industrial Strategy and is led by CEO Penelope ...

. It then later reached peak intensity just northwest of Ireland and then crossed the north of

Scotland Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to th ...

hours later. It hung around the coast of

Norway Norway, officially the Kingdom of Norway, is a Nordic country in Northern Europe, the mainland territory of which comprises the western and northernmost portion of the Scandinavian Peninsula. The remote Arctic island of Jan Mayen and t ...

for the next week before being absorbed by another strong windstorm named

Joachim Joachim (; ''Yəhōyāqīm'', "he whom Yahweh has set up"; ; ) was, according to Christian tradition, the husband of Saint Anne and the father of Mary, the mother of Jesus. The story of Joachim and Anne first appears in the Biblical apocryphal ...

. Hergen was not the first storm to strike Western Europe during the last week as Cyclone Friedhelm brought widespread damage and very strong winds on 8 December. Hergen was followed by Joachim a few days later, then Oliver /Patrick (Cato/Dagmar) during the Christmas holiday.

Cyclone Ulli Cyclone Ulli (also named Cyclone Emil by the Norwegian Meteorological Institute) was an intense European windstorm. Forming on December 31, 2011 off the coast of New Jersey, Ulli began a rapid strengthening phase on January 2 as it sped ...

then brought major damage and flooding to Northern Europe during the early part of January 2012.

Meteorological history

On 11 December 2011, the

had noted a complex

weather system In meteorology, a low-pressure area, low area or low is a region where the atmospheric pressure is lower than that of surrounding locations. Low-pressure areas are commonly associated with inclement weather (such as cloudy, windy, with possible ...

over the central

Atlantic The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the "Old World" of Africa, Europe an ...

, associated with several warm and

cold front A cold front is the leading edge of a cooler mass of air at ground level that replaces a warmer mass of air and lies within a pronounced surface trough of low pressure. It often forms behind an extratropical cyclone (to the west in the Northern ...

s. An amplified jet stream—a strong and fast-moving airstream aloft—advanced eastward, sparking rapid

cyclogenesis Cyclogenesis is the development or strengthening of cyclonic circulation in the atmosphere (a low-pressure area). Cyclogenesis is an umbrella term for at least three different processes, all of which result in the development of some sort of cyc ...

along the fronts. By the following day, a low-pressure centre had developed along an

occlusion Occlusion may refer to: Health and fitness * Occlusion (dentistry), the manner in which the upper and lower teeth come together when the mouth is closed * Occlusion miliaria, a skin condition * Occlusive dressing, an air- and water-tight trauma ...

between two of the fronts. The low rapidly deepened as it approached the

British Isles The British Isles are a group of islands in the North Atlantic Ocean off the north-western coast of continental Europe, consisting of the islands of Great Britain, Ireland, the Isle of Man, the Inner and Outer Hebrides, the Northern Isles (O ...

, with a developing occluded

rainband A rainband is a cloud and precipitation structure associated with an area of rainfall which is significantly elongated. Rainbands can be stratiform or convective, and are generated by differences in temperature. When noted on weather radar ima ...

producing

sustained winds Sustain is a parameter of musical sound in time. Sustain may also refer to: * ''Sustain'' (album), a 2007 album by ska punk band Buck-O-Nine * ''Sustain'' (composition) a 2018 orchestral composition by American composer Andrew Norman * Sustain ...

of up to . It later deepened to a minimum

barometric pressure Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equivalent to 1013.25 millibar ...

of , centred just northwest of Ireland. A wave was recorded off the coast of

County Donegal County Donegal ( ; ga, Contae Dhún na nGall) is a county of Ireland in the province of Ulster and in the Northern and Western Region. It is named after the town of Donegal in the south of the county. It has also been known as County Tyrconn ...

at 1400 UTC on 13 December. On 14 December, Hergen had moved slightly to the northeast while centred just off the coast of the

Shetland Isles Shetland, also called the Shetland Islands and formerly Zetland, is a subarctic archipelago in Scotland lying between Orkney, the Faroe Islands and Norway. It is the northernmost region of the United Kingdom. The islands lie about to the n ...

. By this time, the system had lost its

weather fronts A weather front is a boundary separating air masses for which several characteristics differ, such as air density, wind, temperature, and humidity. Disturbed and unstable weather due to these differences often arises along the boundary. For i ...

. The storm moved slowly offshore Norway for the next few days before being absorbed by the larger Cyclone Joachim on 19 December.

Preparations and warnings

On 10 December, a low pressure system formed over

Labrador , nickname = "The Big Land" , etymology = , subdivision_type = Country , subdivision_name = Canada , subdivision_type1 = Province , subdivision_name1 ...

. This storm rapidly deepened as it moved towards the United Kingdom, which led to the

issuing severe weather warnings. At the time, the forecast storms were considered to be equivalent to a

Category 4 hurricane Category 4 or Category IV may refer to: * Category 4 cable, a cable that consists of four unshielded twisted-pair wires * Category 4 fireworks, British fireworks that are for sale only to professionals * Category 4 tropical cyclone, on any of the ...

on the Saffir-Simpson Hurricane Scale. The storm was only expected to strike parts of England and

Wales Wales ( cy, Cymru ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by England to the Wales–England border, east, the Irish Sea to the north and west, the Celtic Sea to the south west and the ...

. Forecasters at multiple meteorological agencies in the United Kingdom said that snow could fall in southern England which would have been the first of the season. They also said that winds could reach , however, there was not much confidence with this prediction.

Impact

The low brought strong winds and rain to

Hampshire Hampshire (, ; abbreviated to Hants) is a ceremonial county, ceremonial and non-metropolitan county, non-metropolitan counties of England, county in western South East England on the coast of the English Channel. Home to two major English citi ...

, flooding streets and felling trees. In some areas, the winds reached speeds of , just below hurricane force. A tree crashed down onto a home in Winchester, causing heavy damage and almost killing a resident inside. In

Kent Kent is a county in South East England and one of the home counties. It borders Greater London to the north-west, Surrey to the west and East Sussex to the south-west, and Essex to the north across the estuary of the River Thames; it faces ...

, the

Port of Dover The Port of Dover is a cross-channel ferry, cruise terminal, maritime cargo and marina facility situated in Dover, Kent, south-east England. It is the nearest English port to France, at just away, and is one of the world's busiest maritime pa ...

was shut from 10:30 p.m. to 5:30 p.m. GMT on 11–12 December. The Scotland transport minister warned of snow and strong winds which could have led to widespread travel disruption. Icy conditions prevailed in Scotland, Northern Ireland and Northern England early on 13 December. In Norway, a ferry was delayed by 17.5 hours by the large waves caused by the storm, leaving some injured.

References

{{European windstorms Hergen 2011 in the United Kingdom 2011 meteorology Hergen